A power conversion apparatus performs power conversion by allowing switching elements such as a MOSFET or an IGBT to perform a switching operation. At this time, a switching loss occurs to follow the switching operation performed by the switching elements. When the switching loss occurs, the temperature of the switching elements (hereinafter, “element temperature”) rises. Therefore, a cooling device is indispensable to suppressing the element temperature from rising.
The cooling device is generally configured to include fins for cooling the heat generated by the elements. There are many cooling devices based on boiling-refrigerant-type cooling that uses the boiling phenomenon of a refrigerant included therein so as to further enhance cooling capability.
In the cooling device based on the boiling-refrigerant-type cooling (hereinafter, “boiling-refrigerant-type cooling device”), the refrigerant is filled in the fins and boiled by the heat generated by the elements and the evaporated refrigerant is cooled by the cooling air via a condenser, thereby cooling the elements. In this way, the boiling-refrigerant-type cooling device is a cooling device having high cooling capability because of the use of the refrigerant.
Despite the high cooling capability, the boiling-refrigerant-type cooling is known to have properties that boiling is not stable and the operation is unstable in a region in which the heat generated by the elements is low (see, for example, Non Patent Literature 1).